Electrode spacing regulator utilizing a nonlinear reference impedance device



D. JOURNEAUX ELECTRODE SPACING REGULATOR UTILIZING A NONLINEAR June 2, 1953 REFERENCE IMPEDANCE DEVICE Original Filed March 8, 1947 Patented June 2, 1953 ELECTRODE SPACING REGULATOR UTILIZ- ING A NONLINEAR REFERENCE IMPED- ANCE DEVICE Didier Journeaux, Wauwatosa, Wis, assignor to Allis-Chalmers Manufacturing Company, Milwaukee, Wis.

Original application March 8, 1947, Serial No.

733,343, now Patent No. 2,539,912, dated January 30, 1951. Divided and. this application July 1, 1950, Serial No. 171,771

11 Claims.

This invention relates in general to improve ments in electric control systems, and more par ticularly to means for regulating the spacing of consumable electrodes between which current flows through a gaseous or liquid medium. This application is a division of my Patent No. 2,539,912.

Electric current may be caused to flow between a pair of working electrodes through a fluid medium for different purposes such as electrolysis of salts, fusion and refining of metals, or chemical reaction between gases. The flow of current or discharge may take place over a wide range of spacings between the electrodes, but under a given set of operating conditions it is generally found advantageous to maintain the electrode spacing substantially constant. When the electrodes are of a consumable type, it is therefore necessary to readjust their spacing from time to time.

As it is generally not feasible to measure the spacing between the electrodes, the electrode actuating apparatus is frequently controlled in response to the current intensity through the electrodes. The action of such control is based on the assumption that there is a uniform relation between the current intensity and the electrode spacing, and it is therefore disturbed by fluctuations in the voltage of the source supplying current to the electrodes. In polyphase furnaces the current intensity through each pair of electrodes is also dependent upon the spacings of the other pairs of electrodes, so that inaccurate spacing of one pair of electrodes results in unnecessary and improper readjustments of the other pairs.

The above disadvantages may be obviated by controlling the spacing of each pair of working electrodes in accordance with the relative values of the voltage across the electrodes and of the voltage of a suitable standard of reference. The latter may consist of any suitable means or combination of means having a volt-ampere characteristic substantially matching the volt-aim pere characteristic of the discharge between electrodes maintained at the desired spacing.

When the discharge between the electrodes has a nonlinear drooping volt-ampere characteristic, any type of standard of reference having a drooping volt-ampere characteristic may be utilized over a limited range of currents. To obtain the desired electrode spacing over a wide range of I currents, the standard of reference should have a nonlinear drooping volt-ampere characteristic.

The system claimed in the above identified patent, which utilizes a pair of reference electrodes asa standard of reference, provides a highly ac curate and sensitive control for maintaining the desired spacing. However, the volt-ampere characteristic of a given pair of reference electrodes is relatively fixed and consequently in such a system special means must be provided to accurately accommodate for working arcs having varying shapes of volt-ampere characteristics. An additional disadvantage of such systems is that the reference electrodes have a limited life.

These disadvantages can be overcome by utilizing as a standard of reference, means which are extremely rugged and durable and whose voltampere characteristic may be readily varied to accommodate working arcs having varying shapes of volt-ampere characteristics. One of the most suitable of such reference standards is a circuit comprising a source of constant voltage associated with an adjustable nonlinear impedance device having a rising characteristic and traversed by current proportional to the current of the working electrodes. The voltages of the working electrodes and of the standard of reference are measured by suitable indicating instruments or measuring circuits, and the spacing of the working electrodes is varied, either manually or by suitable responsive means, in accordance with the relative values of the measured voltages.

It is therefore an object of this invention to provide a system for regulating the spacing of a pair of electrodes which is extremely rugged and durable.

It is a further object of the present invention to provide a system for regulating the spacing of a pair of electrodes which is accurate for electrodes carrying arcs having varying shapes of volt-ampere characteristics,

It is an additional object of the invention to provide an improved system for regulating the spacing of a pair of arcing electrodes utilizing a standard of reference having a volt-ampere characteristic matching the volt-ampere characteristic of the arc.

Objects and advantages other than those above set forth will be apparent from the following description when read in connection with the accompanying drawing, in which:

Fig. 1 diagrammatically illustrates one em bodiment of the invention for regulating the spacing of a pair of electrodes of a polyphase arc furnace, in which embodiment a nonlinear resistor is utilized as an element of the standard of reference for controlling the electrode hoist motor through an electric valve;

Fig. 2 diagrammatically illustrates an alter- Li nate embodiment of the invention in which one element of the standard of reference is a nonlinear reactor; and

Fig. 3 is .a :graph of the volt-ampere characteristics of the working electrodes and of the elements of the standard of reference.

Referring more particularly to the drawing by characters of reference, numerals H, l2, [-3 desig nate electrodes of an electric furnace is of the polyphase arcing type. Current is supplied to the electrodes from a suitable source of alternating current represented as a three-phasedistribution circuit 5 5 connected with the electrodes through suitable current limiting means such as reactors ft. The furnace contains a pool of molten metal ll serving as an intermediate electrode of which different portions cooperate with elec trodes ll, l2, l3 to constitute three pairs of electrodes.

Electrodes ll, l2, it are severally provided with hoisting-instinct r --maintaining the electrodes'at a constant distance 1 m pool ll. The hoisting means maybe actuated anually, or each electrode may be provided with a hoist motor such as an electric-motor of the direct current type having an armature l9 connected with the electrodethrough a shaft 251.

The opera on of the hoisting mean oielectrode ll is controlled in dependence upon the relative values of the voltage electrodes H, ll an of the voltage across a su ble stan ard of reference. The volt-ampere characte stic of the standard of reference should-be gen-oi ally similar to the volt-ampere characteristic of the are drawn between electrode ii, i? and should therefore generally be-dlOOplllg when the dischargebetweenelectrodes ll, ll i of the type designated as an are. To obtain a control of maximum accuracy the volt-ampere characteristic of the standard of reference should further be nonlinear.

The standard of reference may consist of a circuit comp-rising an adjustable nonlinear resistor 21 and a source which may be adjusted to operate at different values of constant voltage. The currents in the standard of reference and in the voltage measuring circuits maybe of any suitable form. If the measuring circuit is to be operated on directcurrent, a battery 22 may utilizedas thesource of constant voltage. Means are pro i-dc-zd -to supply to resistor .72! current of any suitable form and or intensity in a predetermined relation .to :the current intensity through electrodes 9 i, H and through the are established therebetween. For example, resistor 2i may be supplied withcurrent proportional to the current of electrodes ll, H from the secondary Winding of an adjustable current transformer 2:3 having its primary winding serially connected with electrode ll. The-voltage across resistor 21 is measured by acircuit which, if it is operated on direct current, maycoinprise a rectifier .5 of any suitable known type, a suitable current smoothing means such as a series reactor 26 associated with a shunt capacitor 27, and a voltage divider 28. An adjustable rectified control voltage proportional to the voltage of resistor 2! is thereby made available between a terminal and the tap of voltage divider 28. A voltmeter 29 may be connected between the negative terminal of voltage divider 2B and the negative terminal of battery 22 to obtain a visual indication of the magnitude of the difference between the voltages of voltage divider 28 and of battery 22.

A similar indication of the voltage across elec- 35 and voltmeter The reading of the voltmeter 36 includes the voltage drop in the body of theeleetrodes H, ll and in the portion of the conductors joining the electrode to the pri inary winding of transformer 31, but such voltage .drop is assumed to be negligible compared to the v of he are voltage.

To the sacing of electrodes ll, ll automatically in response to the relative values of the voltages measured by voltmeter-s 29 and 38, armature l 9 may be intermittently supplied with l'GCtifl current from circuit 35 through a transformer and through an electric valve of any suitable typ provided with a control electrode. such as a sh] id yratron 38. The control grid thyratron connected tothecathode l! thereo hrough a. circuit comprising voltdividers cattery 22, and a current limiting resistor Thyra en 33 is therefore responsive to the diil'erence l een the constant voltage or battery 22 and the sum of two control voltages proportional to the voltages acrosselectrodes H, E and reference resistor 2|. The critical potential. above which control grid must be tron t to render thyratron '38 conductive, be writ. by impressing suitable potential on shield grid by means'of a suitable source represented by battery .44.

In oper ion, current supplied to furnace 1 4 flows one of the conductors of circuit l5 through one o actors l5 and electrode H and rear; cent pcrtionof theelectrode T in the form working arc. The current returns to condu "tor of circuit ISthrough anoth on set an another portion of and electrode I; or T3. In genipere characteristic of the are the electrodes M, H, is drooping i urned that the voltsignated #5 in Fig. 3, .is are between electrodes a spacing has the desired the volt r drawn between and nonlinear. am ere chard the characteri value.

If the electrode spacing becomes .too narrow the volt-a1npere characteristic will vdrop to acorresponding extent as shown bycurve :46, Iorexample. If the electrode spacing becomes too wide the volt-ampere characteristic will be boasted a corresponding extent as shown by curve 41, for example. The volt-ampere characteristic of battery 22 is a horizontal line such as line 18 in Fig. 3. The volt-ampere characteristic of resistor 2l is rising. It is curved as shown .by curve 40 of Fig. 3, for example, as the resistor is nonlinear. The resistor may be made of any suitable known material, such as clay bonded silicon carbide sold under the trade-mark Thyrite.

Resistor 2l is so adjusted that when :the ordinates of curve 42 are subtracted from the ordinates of line 48, the resultant curve substantially matches the shape of curve 45. This means that the resultant curve, if it is not substantially identical to curve 45, at least can be rendered substantially identical to curve 4.5 by a change in scale. Therefore battery 22 and resistor 21 are connected in a circuit whose output voltage, as measured by voltmeter 29, is related to the wonking electrode current by a volt-ampere characteristic similar to the volt-ampere characteristic of the working electrodes when the electrodes have a predetermined desired spacing. If the volt-ampere characteristic of the standard of reference is identical to the characteristic of the arc, the voltage measured by voltmeter 29 then is equal to the actual voltage across electrodes H, ll. If the volt-ampere characteristic of the standard of reference merely matches the electrode characteristic, the actual voltage of the arc is reduced or increased through transformer 3| and voltage divider 35 before being compared with the voltage of the standard of reference. Thyratron 38 is therefore diiferentially responsive to the output voltage of the circuit of voltage divider 28 and battery 22 and to a voltage equal to or proportional to the voltage across electrodes H, H.

The voltage appearing across voltage divider 35 is a measure of the voltage actually present across electrodes ll, ll. The voltage appearing between the negative terminal of battery 22 and the negative terminal of voltage divider 28 is a measure of the voltage which would exist between electrodes ll, I! if their spacing had the desired value. If the spacing of electrodes II, I! is correctly adjusted, voltmeters 29 and 36 therefore will always measure equal voltages regardless of the current intensity through electrodes ll, l2, l3 and I1 and regardless of the positions of electrodes I2, 13 with respect to electrode l1. If the spacing of electrodes 1 I, I1 is too wide, voltmeter 29 will have a lower reading than voltmeter 36 and if the spacing is too narrow voltmeter 29 will have a higher reading than voltmeter 36.

If the grid control circuit of thyratron 38 is open, the spacing between electrodes II, I! may be adjusted manually in accordance with the relative values of the voltmeter readings to bring their voltages to equality. When the control grid circuit of thyratron 38 is closed as shown in Fig. l, the potential of grid 39 with respect to the potential of cathode 4| is equal to the difference between the output voltage of the standard of reference and a voltage equal 01' proportional to the voltage of electrodes ll, IT. For the sake of simplicity it will be assumed that the critical potential of grid 39 is equal to the potential of the associated cathode 4 I.

When the spacing of electrodes II, I! is too wide, the voltage dividers and battery 22 bring grid 39 to a potential above the potential of cathode 4|, and thyratron 38 therefore becomes conductive to transmit rectified current to armature [9.

The armature drives shaft 20 to lower electrode l I. As a result of the decrease in the spacing between electrodes I I, [1, the voltage of voltage divider 35 decreases relatively to the voltage of voltage divider 28 regardless of the current intensity through electrodes H, H. The potential of grid 39 is thereby caused to drop and, when such potential is again below cathode potential, thyratron 38 returns to the nonconductive condition and motor l8 stops. If the voltage dividers are properly adjusted the spacing between electrodes ll, I1 will then have the desired value.

The above described control system is operable only to cause motor It to lower electrode II, but it will be understood that the system may also be arranged to cause the motor to raise electrode 1 I when the spacing between electrodes H, H is too narrow. Additional motors and associated control systems will generally be provided for regulating electrodes I2 and I3.

As shown in Fig. 2, resistor 2| of Fig. 1 may be replaced by an adjustable inductive reactor 49. The reactor is provided with an inductive winding 52. Its core may form two magnetic paths which are symmetrically saturated by a bias winding 5!. As a result of the connections of grid 39, thyratron 38 is again additively responsive to the two variable control voltages, of which one is produced in voltage divider 35 in response to the voltage across electrodes II, I! and the other is produced in voltage divider 28 in response to the current flow through electrodes l I, H.

The volt-ampere characteristic of reactor 49 is rising and the volt-ampere characteristic of the combination of current transformer 24, reactor 49, voltage divider 28, and battery 22 is drooping. If reactor 49 is provided with a core in which the magnetic flux reaches the saturation range, the volt-ampere characteristic of the combination is rendered, nonlinear and may be adjusted to approximate curve 45 as in the previously considered embodiment. I

Bias winding 5! is supplied with a variable direct current from a suitable source such as a battery 53 through an adjustable resistor 54. Variations in the current in bias winding 5| act in a well known manner to vary the saturation of the core or reactor 49 to thereby vary the shape of the volt-ampere characteristic of the reactor. Therefore, bias winding 5! provides a means of readily adjusting the volt-ampere characteristic of the standard of reference to accommodate for working arcs having varying shapes of volt-ampere characteristics.

Although but two embodiments of the present invention have been shown and described, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the spirit of the invention or. from the scope of the appended claims.

It is claimed and desired to secure by Letters Patent:

1. In a control system for a pair of relatively movable electrodes between which current is flowing in the form of an are having a predetermined nonlinear volt-ampere characteristic when the spacing between said electrodes has the desired value, the combination of a motor for controlling the spacing of said electrodes, a resistor having a nonlinear volt-ampere characteristic, means for supplying to said resistor a current proportional to the current flowing through said electrodes, a source of constant voltage, means for connecting said source and said resistor into a circuit having an output voltage related to said electrode current by a volt-ampere characteristic substantially matching said predetermined voltampere characteristic, and means responsive to the difference between said output voltage and a voltage proportional to the voltage across said electrodes for controlling the operation of said motor.

2. In a control system for a pair of relatively movable electrodes between which current is flowing in the form of an are having a predetermined nonlinear volt-ampere characteristic when the spacing between said electrodes has a predetermined value, the combination of a motor for controlling the spacing of said electrodes, an impedance device having a nonlinear volt-ampere characteristic, means for supplying to said device ing through said electrodes, voltage i constant voltage connec ed to said voltage flowing in the formof anarohavlnge mined nonlinear volt-ampere characteristic when the spacing between the said electrodes has .a predet output voltage related :to said electrod by a volt-an1pere characteristic substantially identical characteristic, and rhesus differen ially trodes -motor.

a current proportional to the current flowing through .said electrodes, a source of constant voltage, means for connecting said sourceand said device'into'a circuit having an output-voltage related to said electrode currentby a voltarnpere characteristic substantially :znatching said predetermined volt-ampere characteristic, and'ineans responsive to the differcn ehetween said output voltage and a voltage proportional to the voltage across'said'electrodes forcontroling .the operation of said motor.

3. In a control-system for a-pair of relatively movable electrodes between which current is flowing iii-the form of an are having; a. predetermined nonlinear volt-ampere characteristic .xvhon the spacinghetween said electrodes has a 'pre determined value, the combination of motor for controlling th spacing oi saidielectrcdes an i npedance device having-a 1101111116121-VC1lh-filllp8l6 characteristic, means for supplying to said tievice current proportional to the .current ow- ..der means connected across said device. sourceoi rider means to produce anoutpzt voltage i to the voltage of said source less the voltage a portion sai voltage divider means, said out-- put voltage being" related to said eletrode current by a volt-ampere characteristic .sufostam ,inotor.

4. In a controlsysternfor a pair of relatively movable electrodes oetween which cur-"em i5;

edeterined value, the combination oi u. controlling-the spacing of said-electrodes, an impedancetdc hil ig; nonlinearvolt-ainpere characteristic, means for supplying to said devicea current proportional to the current flowing; through said electrodes, a. sourceoi constant voltage, means for connecting said source and said device into a circuithaviuc niotor f0;

sive to said output voltage and to t e'vo across said electrodes -for controlling the 0' tion of said motor.

5. In a control system for a pair oi relatively movable electrodes oetw en which current is flowing in the form of an are having a predetermined nonlinear volt-ampere characteristic when the spacing between the said electrodes has a predetermined value, the combination ore in for controllir ntnespacing of said tro resistor having a nonlinear volt-ampere characteristic, means or supplying to said resistor a current proportional .to the current through electrodes, a source of constant voltage, means liar-connecting said source and said-device into circuit having ancutput vol age relatziad to said electrode current .bya voltam :ere characteristic substantially identical to said predetermined volt-ampere characteristic,

and means differentially responsive to :said output voltage and to ithe .voltageacrosssaid elecfor controlling .the operation of said movable ,electr flowing in the teirnined volt-airport; spacing betweensaid electrodes has apredeterinineol veluethe conioination of a motor for conuance dew characteristic, means for supplying to saiddevice 6.1113, control system for a pairof relatively movable electrodes between which current is flOWlIlg in the form of an arc having a predete niined nonlinear volt-ampere characteristicwhen the spacing between said electrodes hasa predetermined value, the combination of a motor for controlling the spacing of said electrodes, a saturaiile reactor having a nonlinear volt-anipere charac eristic, means for varying the volt- .ampere characteristic of said reactor, means for supplying to saidreactor a current proportional to thecurrent flowing through saidelectrodes, a source of constant voltage, means for connecting said-sourceand eactor into a circuit having an output voltage related to said electrode current by a volt-an1pere characteristic substantially identical to said predetermined volt-ampere characteristic, means responsive to the difference between said output voltage and the voltage across said electrodes for controlling the operation of said motor.

7 .In acontrol system for a pair of relatively movable electrodes he en which current is flowing in the form of an are having a predetermined nonlinear volt-:|.rnpeie characteristic when the spaci between said electrodes has a predetermined ulue, the combination of a motor controll' the spacing; of said electrodes, 9.

Lion of said motor.

for a pair of relatively "sen which current is of an having-a predevolt-ampere characteristic ensaid electrodes has a value. the combination ofa motor the spacing of said electrodes, a rr- .ctcr having a noilinear volt-ampere means for supplyingto said reacro orticnal to the current flowing controlling the l 3. In a contr i odes, a-source of constant voltage a .s for connecting sai source and said rea uit havin an output voltage related to ctrode crr rent by a volt-ampere .charac c substantially matching said predetc lied volt-anipere characteristic, and means responsive to the difference between said output and a voltage proportional to the voltage across said electrodes for controlling the operation of said motor.

'9. In a control system for pair of relatively movable electro between which current is flowing in the to n of an arc having a predecharacteristic when the trolling th spaci:

7 of said having a electrodes, an impednonlinear volt-ampere an alternating current proportional to the current flowing through said electrodesa source 01 constant unidirectional volta e, means for-connesting said source and said device intoa circuit having an output voltage related to said electrode current by a volt-ampere characteristic substantially matching said predetermined volt-ampere characteristic comprising a rectifier connected across said device and a voltage divider connected across said rectifier to be energized at a unidirectional voltage proportional to the voltage of said device, and means responsive to the difference between the said output voltage and a rectified voltage proportional to the voltage across said electrodes for controlling the operation of said motor.

10. In a control system for a pair of relatively movable electrodes between which current is flowing in the form of a working are having a predetermined volt-ampere characteristic when the spacing between said electrodes has a predetermined value, the combination of a motor for controlling the spacing of said electrodes, an impedance device having a nonlinear volt-ampere characteristic, means for supplying to said device an alternating current proportional to the current through said electrodes, a rectifier connected across said device, a voltage divider having an adjustable tap and a pair of terminals connected to said rectifier, a source of constant unidirectional voltage, means for connecting the positive terminal of said source to said tap to produce between the negative terminal of said voltage divider and the negative terminal of said source an output voltage related to said electrode current by a volt-ampere characteristic substantially matching said predetermined volt-ampere characteristic, and means responsive to the diiference between said output voltage and a rectified voltage proportional to the voltage across said electrodes for controlling the operation of said motor.

11. In a control system for a pair of relatively movable electrodes between which current is flowing in the form of an are having a predetermined nonlinear volt-ampere characteristic when the spacing between said electrodes has a predetermined value, the combination of a motor for controlling the spacing of said electrodes, an impedance device having a nonlinear volt-ampere characteristic, first means for supplying to said device a current proportional to the current flowing through said electrodes, a source of constant unidirectional voltage, second means connected to said device for producing a first variable unidirectional voltage proportional to the voltage of said device, third means connected to said electrodes for producing a second variable unidirectional voltage proportional to the Voltage across said electrodes, and means for controlling the operation of said motor comprising means connected to said source and to said second and third means responsive to the difference between the voltage of said source and the sum of said variable unidirectional voltages.

DIDIER J OURNEAUX.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,259,985 Levy Oct. 21, 1941 2,276,644 Blankenbuehler Mar. 17, 1942 2,518,580 Trofimou Apr. 15, 1950 

